Docker Images! WTH is that?
Ep:02 Hands-on Docker Images commands and usage
I hope you guys are doing well.
Docker Images are the template that contains set of instructions for creating a container.
Fair enough? I don’t think so.
Docker Images is the combination of all the scripts that is required for your application to run.
Docker Files are used to create docker images using set of available docker commands, lets dive into those commands to create an image and upload to a registry and also try to pull it and run a container. :D Excited?
*** Let’s Start ***
- List the available images on the host
...$ docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
ubuntu latest f643c72bc252 2 weeks ago 72.9MB
hello-world latest bf756fb1ae65 11 months ago 13.3kB
- Get the detailed information of the image like image name, full id, container details, registry details etc.
Use the image name or the image id with the command exposed .
...$ docker inspect ubuntu
[
{
"Id": "sha256:f643c72bc25212974c16f3348b3a898b1ec1eb13ec1539e10a103e6e217eb2f1",
"RepoTags": [
"ubuntu:latest"
],
"RepoDigests": [
"ubuntu@sha256:c95a8e48bf88e9849f3e0f723d9f49fa12c5a00cfc6e60d2bc99d87555295e4c"
],
"Parent": "",
"Comment": "",
"Created": "2020-11-25T22:25:29.546718343Z",
"Container": "0672cd8bc2236c666c647f97effe707c8f6ba9783da7e88763c8d46c69dc174a",
"ContainerConfig": {
"Hostname": "0672cd8bc223",
"Domainname": "",
"User": "",
"AttachStdin": false,
"AttachStdout": false,
"AttachStderr": false,
"Tty": false,
"OpenStdin": false,
"StdinOnce": false,
"Env": [
"PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
],
"Cmd": [
"/bin/sh",
"-c",
"#(nop) ",
"CMD [\"/bin/bash\"]"
],
"Image": "sha256:28e90b4e135b38b4dd5efd0045019a2c8bfb7e114383e3a4ae80b1ec0dcaaf79",
"Volumes": null,
"WorkingDir": "",
"Entrypoint": null,
"OnBuild": null,
"Labels": {}
},
"DockerVersion": "19.03.12",
"Author": "",
"Config": {
"Hostname": "",
"Domainname": "",
"User": "",
"AttachStdin": false,
"AttachStdout": false,
"AttachStderr": false,
"Tty": false,
"OpenStdin": false,
"StdinOnce": false,
"Env": [
"PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
],
"Cmd": [
"/bin/bash"
],
"Image": "sha256:28e90b4e135b38b4dd5efd0045019a2c8bfb7e114383e3a4ae80b1ec0dcaaf79",
"Volumes": null,
"WorkingDir": "",
"Entrypoint": null,
"OnBuild": null,
"Labels": null
},
"Architecture": "amd64",
"Os": "linux",
"Size": 72898198,
"VirtualSize": 72898198,
"GraphDriver": {
"Data": {
"LowerDir": "/var/lib/docker/overlay2/25f72d93acb934405b2b479b3a74be42a6c38b903305534e20d3978c3a0f9d4b/diff:/var/lib/docker/overlay2/146989b9b288c76d53f3af5188ec829ffbbf98eb4df5fd604e6423c8d502b009/diff",
"MergedDir": "/var/lib/docker/overlay2/287d5fb4298c98c16cfbb149ae7706e08eb0544d4696961698500a7d9b45c3e8/merged",
"UpperDir": "/var/lib/docker/overlay2/287d5fb4298c98c16cfbb149ae7706e08eb0544d4696961698500a7d9b45c3e8/diff",
"WorkDir": "/var/lib/docker/overlay2/287d5fb4298c98c16cfbb149ae7706e08eb0544d4696961698500a7d9b45c3e8/work"
},
"Name": "overlay2"
},
"RootFS": {
"Type": "layers",
"Layers": [
"sha256:bacd3af13903e13a43fe87b6944acd1ff21024132aad6e74b4452d984fb1a99a",
"sha256:9069f84dbbe96d4c50a656a05bbe6b6892722b0d1116a8f7fd9d274f4e991bf6",
"sha256:f6253634dc78da2f2e3bee9c8063593f880dc35d701307f30f65553e0f50c18c"
]
},
"Metadata": {
"LastTagTime": "0001-01-01T00:00:00Z"
}
}
]
3. Pull images from a registry using this command,
...$ docker image pull centos:latest
latest: Pulling from library/centos
7a0437f04f83: Pull complete
Digest: sha256:5528e8b1b1719d34604c87e11dcd1c0a20bedf46e83b5632cdeac91b8c04efc1
Status: Downloaded newer image for centos:latest
docker.io/library/centos:latest... $ docker image ls //verify it using this command
REPOSITORY TAG IMAGE ID CREATED SIZE
centos latest 300e315adb2f 5 days ago 209MB
ubuntu latest f643c72bc252 2 weeks ago 72.9MB
hello-world latest bf756fb1ae65 11 months ago 13.3kB
In the above example, we just pulled the CentOS from dockerhub.com.
- Log into the image using the following steps,
...$ docker run -it centos bash //remember to use ctrl+p ctrl+q,
[root@26114b36d46f /]# ls // to keep the container running
bin dev etc home lib lib64 lost+found media mnt opt proc root run sbin srv sys tmp usr var
...$ docker ps //verify the container is running using this command
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
26114b36d46f centos "bash" About a minute ago Up About a minute gifted_jemison
- Remove a image from our host , follow with me,
...$ docker rmi 300e315adb2f
Error response from daemon: conflict: unable to delete 300e315adb2f (cannot be forced) - image is being used by running container 26114b36d46f
Saw the above error? Reason the container is still running so image cannot be removed.
...$ docker ps //verify the container is running using this command
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
26114b36d46f centos "bash" About a minute ago Up About a minute gifted_jemison...$ docker stop 26114b36d46f // name or container Id can be given.
26114b36d46f...$ docker ps // verify that the container is stopped
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES//Try to delete now$ docker rmi 300e315adb2f
Error response from daemon: conflict: unable to delete 300e315adb2f (must be forced) - image is being used by stopped container 26114b36d46f
In the last log, if you can see after stopping the container , we tried to delete the image, notice now it’s asking us to remove it forcefully reason being that the docker was running and its context is still saved in host (be careful while performing this action). We can delete it with force using the below command,
...$ docker rmi -f 300e315adb2f //Name/container Id can be used
Untagged: centos:latest
Untagged: centos@sha256:5528e8b1b1719d34604c87e11dcd1c0a20bedf46e83b5632cdeac91b8c04efc1
Deleted: sha256:300e315adb2f96afe5f0b2780b87f28ae95231fe3bdd1e16b9ba606307728f55...$ docker images //verify that the image is deleted now
REPOSITORY TAG IMAGE ID CREATED SIZE
ubuntu latest f643c72bc252 2 weeks ago 72.9MB
hello-world latest bf756fb1ae65 11 months ago 13.3kB
- Also you can save the image in tar and can load it anytime, anywhere.
...$ docker image save -o hello-world.tar hello-world:latest//to verify do ls -lrt$ ls -lrt .-rwxrwxrwx 1 meghal meghal 24576 Dec 13 22:35 hello-world.tar
to load this tar as an image, follow these simple step,
...$ docker images // you can see, we don't have hello-world image
REPOSITORY TAG IMAGE ID CREATED SIZE
ubuntu latest f643c72bc252 2 weeks ago 72.9MB...$ docker load -i hello-world.tar // give the tar name here
Loaded image: hello-world:latest...$ docker images // verify that the image is present
REPOSITORY TAG IMAGE ID CREATED SIZE
ubuntu latest f643c72bc252 2 weeks ago 72.9MB
hello-world latest bf756fb1ae65 11 months ago 13.3kB
- Rename the tag name of an image from latest to custom tag name
...$ docker tag hello-world:latest hello-world:version1$ docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
ubuntu latest f643c72bc252 2 weeks ago 72.9MB
hello-world latest bf756fb1ae65 11 months ago 13.3kB
hello-world version1 bf756fb1ae65 11 months ago 13.3kB
We can see, two images with different tag name are present, reason is we have tagged it locally, you can push this to the registry to replace it, using the following command.
...$ docker push hello-world:version1
The push refers to repository [docker.io/library/hello-world]
9c27e219663c: Layer already exists
- Note I’m not allowed to push it since I’m using hello-world image. If it’s your custom image , you would be able to do this.
That’s all for today, I hope you learnt to play around with container, Next up we will learn about image commands in docker.
Please take a minute to appreciate your efforts. You made it. Learnt something new. :) Congratulations
Article 1 : Hello World Docker
Article 2 : Docker Terminologies
Article 3 : Docker Basic Commands. PS Cheat Sheet Ep-01
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Stay tuned , Keep Learning. Cheers :D
